1. Field of the Invention
This invention relates to a resin-sealed semiconductor device and its lead frame.
2. Description of the Prior Art
A lead frame including a heat spreader is used to make a resin-sealed semiconductor device carrying a semiconductor chip which generates a relatively large amount of heat in the order of 1 to 2 W. The heat spreader has a sufficiently large area, as compared with that of the semiconductor chip, to maintain its thermal resistance at a low level. The semiconductor chip is bonded to the central portion of the heat spreader by a bondng material of good thermal conductivity, such as a low-melting brazing alloy or conductive adhesive. A multiplicity of metal leads are fastened to the outer edge of the heat spreader by an insulating material, which is usually of a polyimide resin, and an adhesive. Bonding wires, such as of gold, are connected between the chip and the inner ends of the leads. The heat spreader and the chip are enclosed in a casing molded from a resin.
A semiconductor chip of the type which generates a relatively large amount of heat has also come to be more highly integrated, and a package of the dual inline type has come to be replaced by one of the guad flat type with a large number of terminals. There already exists even a package having more than 100 terminals, or leads. The provision of a large number of leads necessitates a smaller lead width and a smaller lead pitch if the package size remains unchanged. A package having 160 leads, for example, has an inner lead pitch which is as small as about 0.23 mm.
Such a small lead pitch, however, makes it difficult for a resin, such as an epoxy resin, to flow satisfactorily through the clearance between every two adjoining leads, and makes it necessary to use a mold having two injection ports on its side facing the chip and on its side facing the head spreader, respectively. Such a mold is, however, undesirably complicated in construction, and expensive.